System for detecting linear dimensions of mechanical workpieces, with wireless signal transmission units

ABSTRACT

A system for detecting linear dimensions of mechanical workpieces includes a checking probe with detecting devices, a power supply and a remote transceiver unit. A stationary transceiver unit is located at a distance from the probe, and is adapted for wireless receiving and transmitting to the remote transceiver unit signals, for example, coded optical signals. The stationary unit transmits activation and/or deactivation signals to the probe for controlling the full power supply of the probe circuits, and/or the return to a “stand-by” power state. The remote transceiver unit includes devices adapted for achieving an automatic sensitivity control and other attenuation devices for preventing unwanted consumption of the probe battery energy due to noise signals. Such noise signals could come from fluorescent lamps, for example, causing improper activation and deactivation of the probe circuits.

TECHNICAL FIELD

The present invention relates to a system for detecting lineardimensions of a workpiece, including a checking probe with detectingdevices, a power supply connected to the checking probe, a remotetransceiver unit, integral with the probe, connected to the detectingdevices and to the power supply, and adapted for wireless transmittingsignals indicative of the state of the probe, and a stationarytransceiver unit, adapted for wireless transmitting activation signalsto the formerly mentioned remote unit, wherein the remote transceiverunit includes receiving devices adapted for receiving the wirelesstransmitted signals, a processing section, connected to the receivingdevices, and to the power supply and adapted for generating an enablesignal, the processing section including at least an amplifier connectedto the receiving devices for outputting an amplified signal, a switchingunit connected to the processing section and to the power supply, andadditional sections, with generating and transmitting circuits,connected to the switching unit, the switching unit being adapted forreceiving the enable signal and, on the basis of this signal,controlling the power supply of at least some of the additionalsections.

BACKGROUND ART

There are known measuring systems as, e.g. systems in numerical controlmachine tools, for detecting the position and/or the dimensions ofmachined workpieces by a contact detecting probe, mounted in themachine, that, in the course of a checking cycle, displaces with respectto the workpiece, touches the surfaces to be checked and responds tocontact by wireless transmitting signals to a receiving unit, usuallylocated at a certain distance from the probe.

The receiving unit is in turn connected, by means of an interfacedevice, to the numerical control unit that, by processing other signalsindicative of the spatial position of the probe, provides informationabout the position of the workpiece surfaces.

The contact detecting probe can include electric batteries for the powersupply of contact detecting circuits and the wireless transmissiondevices. The wireless transmission can take place, for example, byemitting electromagnetic signals of optical or radio-frequency type.Since the probe is utilized just for short time intervals during themachining cycle of the machine tool, the associated detecting circuitsand transmission devices are normally kept in a “stand-by” state of lowpower consumption and powered-up only when there is the need to performa checking cycle. The switching from the “stand-by” state to the full“powered-up” state can be accomplished by controlling suitable switchingdevices on the probe by means of activation signals wireless transmittedby the receiving unit. When the measuring cycle ends, the probe circuitsreturn to the “stand-by” state of low power consumption either bywireless transmitting a suitable deactivation signal, or, as analternative, after a predetermined time period has elapsed.

U.S. Pat. No. 4,779,319 discloses a measuring system with thesecharacteristics and more specifically it describes a checking probe withcircuits for transmitting optical signals in the infrared band. Aninfrared radiation flash is utilized for activating the probe, in otherwords for controlling the full power-up of the probe detecting circuitsand the transmission devices.

The probe circuits for receiving the optical activation signal andcontrolling the connection to the batteries include a receiver diode anda coil that, among other things, serves as a high pass filter forreducing the negative effects due to the steady state and/or lowfrequency components of the environment illumination and for excludingfrom subsequent processings low frequency pulses emitted, for example,by fluorescent lamps located in the probe environment.

However, it may occur that the fluorescent lamps, or other sources oflight, emit electromagnetic radiations with frequencies in the same bandas the activation or deactivation signals (or, more specifically, theassociated modulating signals) and that these radiations cause theunwanted activation of at least some of the probe circuits, and auseless consumption of the battery supply energy, or the unwanteddeactivation in the course of a checking cycle and imaginable negativeconsequences.

A fluorescent lamp can emit improper and unforeseeable radiations, evenin the infrared radiation band, that vary depending on the type of lamp,on the environment temperature, on the power supply voltage, on the ageand the efficiency conditions of the lamp itself.

Another possible way for probe optical activation (or deactivation)foresees, as an alternative to the pulse signal described in patent U.S.Pat. No. 4,779,319, an infrared radiation signal modulated as a sequenceof pulses of a given frequency (for example, about ten KHz) andtransmitted to the receiving unit for a determined time period (forexample, a few tenths of a second). The probe circuits include a logicsection—that is powered when there is detected a signal of sufficientintensity—that checks whether the received signal has the requiredfrequency and minimum duration (a number of pulses generally by farsmaller than those actually transmitted) of the activation (ordeactivation) signal and that, in the affirmative, causes the power-upof the other probe circuits (or the return to the stand-by state).

The intensity of the radiations randomly emitted by the fluorescentlamps in the frequency band of the activation signal can be sufficientfor causing the frequent and needless power-up of the logic section ofthe probe circuits, and consequently unwanted consumption of the batteryenergy. Furthermore, while the logic section is improperly powered, itmay occur that a sequence of pulses be sent by a fluorescent lamp whosefrequency and duration are the same as those of the activation signal.It may also occur that, while the probe is performing a checking cycle,the logic section detects a sequence of pulses having frequency andduration that match those of the deactivation signal, without the lattersignal having actually been transmitted by the receiving unit.

DISCLOSURE OF THE INVENTION

Object of the present invention is to overcome the inconveniences, interms of consumption of the battery supply energy and undesired probeactivation or deactivation, caused by fluorescent lamps, or by othersources emitting electromagnetic radiations in the probe environment.

This and other objects are achieved by a system in which the processingsection of the remote transceiver unit includes attenuation devicesadapted for inhibiting the generating of the enable signal on the basisof attributes of the signal that the receiving devices have wirelessreceived, the attenuation devices including elements of a feedbackcircuit for attenuating the intensity of said amplified signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is hereinafter described in detail with reference to theenclosed sheets of drawings, given by way of non limiting example only,wherein

FIG. 1 is a schematic view of a machine tool on which there is mounted achecking probe for detecting linear dimensions of mechanical pieces;

FIG. 2 is a diagram including some blocks of a known transceiver unit ofcoded optical radiations;

FIGS. 3 and 4 show the trends of some of the signals generated in thetransceiver unit of FIG. 2 on the arrival of a probe activation signalor a noise signal;

FIG. 5 is a diagram including some blocks of a transceiver unit of codedoptical radiations, according to a first embodiment of the invention;

FIGS. 6, 7 and 8 show the trends of some of the signals generated in thetransceiver unit of FIG. 5 on the arrival of a noise signal, anactivation signal or a deactivation signal;

FIG. 9 is a circuit diagram of a component of the transceiver unit ofFIG. 5, according to a different embodiment of the invention; and

FIG. 10 is a schematic and partial view of a transceiver unit of codedoptical radiations, according to a further embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 illustrates, in simplified form, a system for detecting lineardimensions of a piece 1 on a machine tool, for example a machiningcenter identified in the drawing by reference number 2, where piece 1 ismachined. The system includes a computerized numerical control 3, forcontrolling the operation of machine tool 2, and a detecting apparatusincluding a checking probe 4. The latter, for example a contactdetecting probe, has a support and reference portion 5 coupled to slidesof machine tool 2, a feeler 6 and an arm 7 carrying feeler 6 and movablewith respect to support portion 5. Moreover, probe 4 includes detectingdevices, for example a microswitch 13, a power supply with a battery 12and a remote transceiver unit 8 for transmitting infrared opticalsignals to and receiving infrared optical signals coming from astationary transceiver unit 10, located at a distance from probe 4.

The stationary transceiver unit 10 is connected, through a cable 9, toan interface unit 11, in turn connected to the computerized numericalcontrol 3. The stationary transceiver unit 10 has the function oftransmitting coded optical signals to the remote transceiver unit 8associated with the probe 4, for activating and deactivating probe 4 inresponse to the reception of a request sent by numerical control 3through the interface unit 11, and receiving, from remote unit 8, codedoptical signals including information about, for example, the spatialposition of feeler 6 with respect to support portion 5, or the level ofcharge of battery 12 of probe 4. The terms activation/deactivation meanthe switching of the power supply of probe 4 from/to a “stand-by” statein which just some low consumption sections of the remote transceiverunit 8 are powered, to/from a state of “full” power-up of unit 8.

FIG. 2 is a block diagram showing some parts of a remote transceiverunit 8 of a known type. It includes receiving devices with a photodiodePH, adapted for receiving the periodic optical signals sent bystationary unit 10, and generating an alternating signal (for example acurrent), a processing section E, and further sections, with a logicprocessing unit (or “logic”) L and circuits for generating andtransmitting optical signals. The latter circuits are schematicallyshown in FIG. 2 by the block identified by letter T, and are achieved ina known way that is not of specific interest to this invention.

In turn, the processing section E, connected to battery 12 andcharacterized by a very low consumption of current, includes anamplifier A1 connected to photodiode PH for generating a signal—forexample a periodic signal and more specifically an alternating voltageVA1—, and a comparator C1, for comparing the amplitude of signal VA1with a first threshold value VTH1 for generating a signal VC1 consistingof a sequence of pulses with frequency and duration that correspond tothose of the periodic signal that stationary unit 10 sends to photodiodePH. Furthermore, processing section E also includes a filter F1 with itsinput connected to comparator C1, and its output connected to a secondcomparator C2, the latter comparing signal VF1 provided by filter F1with a second threshold value VTH2. Furthermore, remote transceiver unit8 includes a circuit G1 that achieves a logic OR, a circuit G2 thatachieves a logic AND and a switching unit A connected to battery 12, tologic L and to circuits T.

When photodiode PH receives an optical signal arriving from stationarytransceiver unit 10, it generates a signal that is amplified byamplifier A1 (VA1 in FIG. 3), and is compared with threshold value VTH1by comparator C1. When the amplitude of signal VA1 is smaller thanthreshold VTH1, output VC1 of comparator C1 is at low logic level, whileit switches to high logic level when the amplitude of signal VA1 exceedsthreshold VTH1. The processed signal VC1, provided by comparator C1 andsent to the input of low pass filter F1, is a sequence of pulses havingthe same frequency and duration (i.e. number of pulses) as the signaltransmitted to photodiode PH. The signal VF1, at the output of filterF1, is then compared by comparator C2 with the threshold value VTH2.When signal VF1, outputted by filter F1, exceeds threshold value VTH2,enable signal VC2, outputted by comparator C2, switches from low to highlogic level and, through the logic OR G1, enables (VG1) switching unit Ato connect battery 12 to logic L in order to provide the latter with thepower supply voltage VA.

The high logic level of signal VC2, through the enable device achievedby means of the logic AND G2, also enables the transmission of theprocessed signal VC1 to logic L, for checking the frequency and theduration of the signal VC1 and, consequently, of the signal received byphotodiode PH. If the detected frequency and duration (i.e. the minimumnumber of pulses) correspond to those of the activation signal, logic Lplaces the signal VL at high logic level for controlling switching unitA to power supply the generating and transmitting circuits T andconcurrently, through logic OR G1, keeps logic L powered even after theactivation signal ends and signal VC2 switches to low logic level.

Logic L brings signal VL back to low logic level when the photodiode PHreceives a deactivation signal, that logic L recognizes by identifyingthe frequency and the duration (minimum number of pulses) of thecorresponding signal VC1.

As an alternative, the switching of signal VL to low logic level can becontrolled when the time set in a timer, achieved in a known way inlogic L and not shown in the figures, elapses. When signal VL switchesto the low logic level, switching unit A is actuated for inhibiting thepower supply of circuits T and, when the received signal is no longerpresent, logic L.

FIG. 3 shows the trends of the above mentioned signals when the circuitsof probe 4 are in a stand-by state and photodiode PH receives anactivation signal transmitted by stationary unit 10. It should berealized that, for the sake of clarity, the unit of division of the timescale in the first two graphs in FIG. 3, relating to signals VA1 andVC1, is of approximately two order: of magnitude smaller than the unitof division of the other graphs (for example: one millisecond in thefirst two graphs, as compared to one tenth of a second in the othergraphs). In this connection, it should be realized that the dimensioningof filter F1, and more particularly its associated time constant RC1, issuch that signal VF1 reaches and exceeds threshold value VTH2 ofcomparator C2 only after a sequence of some hundredths of pulses ofsignal VC1. In practice, the stationary transceiver unit 10 transmits anactivation (or deactivation) signal with a very high number of pulses(in the range of some thousandths), and logic L must identify just alimited sequence thereof (normally just a little more than about tenpulses). For the same reason, the first two graphs of FIG. 3,specifically those relating to signals VA1 and VC1, have interruptions.

The function of filter F1 and comparator C2 is to power supply logic Lonly when the mean value of signal VC1 outputted by comparator C1 or,more specifically, its “duty-cycle” (i.e., the ratio between thetime—within a cycle—in which said signal assumes a high logic level andthe duration of the whole cycle), exceeds a specific value in a ratherlong time interval, thereby monitoring that photodiode PH has received asignal that exceeds the minimum predetermined values in terms ofintensity and duration. In this way it is possible to prevent a needlessconsumption of the battery supply energy when there are pulse opticalnoises or activation signals that are too weak for being correctlyprocessed by logic L.

In the event that fluorescent lamps, or other sources of electromagneticwaves near probe 4, emit accidental and unforeseeable infraredradiations, the intensity and duration of such radiations can besufficient for keeping logic L powered up for long periods (i.e. VAremains at high logic level), and cause a consequent considerableincrease in the consumption of energy of battery 12.

FIG. 4 shows the trends of the same signals that are shown in FIG. 3,under the circumstance wherein photodiode PH receives a signal that isnot identified by logic L as an activation/deactivation signal (forexample, a noise signal, the end of which is not shown in FIG. 4).

These signals have the same trend as those previously shown, but in thiscase, signal VL, outputted by the logic L, remains at low logic level.According to what is shown in FIG. 4, when the intensity of the signalsreceived by photodiode PH remains greater than a predetermined valuelogic L remains powered for identifying the frequency and the durationof the received signal. As a consequence, there is a consumption ofenergy of battery 12 even at times when the circuits could remain in astand-by state.

FIG. 5 is a block diagram showing some parts of a remote transceiverunit 8 according to a first embodiment of the invention.

The processing section E includes, in addition to the componentsdescribed with reference to FIG. 2, attenuation devices that achieve anautomatic sensitivity control and that, in the illustrated example,include elements of a feedback circuit, more specifically an additionallow pass filter F2, the input of which is connected to the output ofcomparator C1, an additional amplifier, for example a differentialamplifier, A2, connected to the output of filter F2, and a field effecttransistor, or MOSFET (Metal Oxide Semiconductor Field EffectTransistor) MF1 of the enhancement mode type that achieves anattenuation device. The zones of transistor MF1 known as “gate”,“source” and “drain” are connected to the output of amplifier A2 and atthe ends of photodiode PH, respectively.

The signal VC1, outputted by comparator C1, is sent to the input offilter F2 that, as more detailedly described hereinafter, also providesa delay generator, having a time costant RC2 longer than that (RC1) offilter F1. The output signal VF2 is compared with a threshold valueVTH3, lower than VTH2, and amplified for providing a signal, moreparticularly a voltage VA2 that is sent to the gate of transistor MF1.Voltage VA2 controls, in an analogue or continuous way, the conductionof transistor MF1 and the consequent, partial, attenuation of the signalgenerated by photodiode PH that reaches amplifier A1. As hereinaftermore clearly explained, this portion of the circuit prevents noisesignals—with intensity and duration equal to or greater than those of anactivation signal—arriving for example from a fluorescent lamp, fromcausing the unwanted and prolonged power supply of logic L.

The operation of the circuit shown in FIG. 5 is now explained withreference to FIGS. 6, 7 and 8 that illustrate the trend of the signalsin three different circumstances. In FIGS. 6, 7 and 8 too, for the sakeof simplicity and clarity, the graphs representing signals VA1 and VC1have interruptions and a different time scale with respect to the othergraphs.

By assuming that, at a specific moment in time, transistor MF1 issubstantially held off (i.e. voltage VA2 is held at low level)—becausephotodiode PH has not received any previous signals—and the circuits arein a stand-by state, the arrival of a signal with sufficient intensityand duration received by photodiode PH generates a sequence of pulsesVC1 (see FIG. 6) that, initially, is similar to the sequence of FIG. 4.

The signal VC1 is sent to both filters F1 and F2 and, because filter F1has a time constant lower than that of filter F2, before value VF2reaches threshold VTH3, the power supply of logic L is enabled and so isthe checking of the frequency and the duration of sequence VC1: if thesignal that photodiode PH has received and, as a consequence, signal VC1do not have the attributes in terms of frequency and duration (minimumnumber of pulses) of an activation signal, signal VL remains at lowlogic level and the circuits T for generating and transmitting opticalsignals are not powered.

When signal VF2 reaches the threshold value VTH3 after a limited delaytime t1 (for example, a few tenths of a second) and, after another veryshort delay time, the voltage level of the signal VA2 provided byamplifier A2 is sufficiently high, transistor MF1 starts to conduct,thereby causing an attenuation of the voltage across source and drain.

Therefore, as soon as transistor MF1 starts to conduct, the amplitudesof the signals at the input and at the output of amplifier A1 arereduced. As a consequence, the duty-cycle of signal VC1, outputted bycomparator C1, reduces owing to the fact that the time intervals inwhich the amplitude of VA1 exceeds the threshold value VTH1 becomeshorter. Thus, output voltage VF1 of filter F1 decreases and stabilizesat a value that is slightly higher than the threshold value VTH3 (andthus lower than the value of VTH2). The output voltage VF2 alsostabilizes at this value so as to keep voltage VA2 sufficiently high,and thus the voltage at the input of amplifier A1 suitably attenuated.When the value of voltage VF1 becomes lower than the threshold valueVTH2 of comparator C2, the value of signal VC2 switches to low logiclevel and, if an activation signal has not been identified in themeantime, the power supply VA of logic L is inhibited and remains so aslong as the noise signals persist (or when these signals stop), therebypreventing a needless consumption of the energy of battery 12.conversely, if the activation signal is in the meantime identified, thesubsequent switching of the value of signal VL to a high level ensuresthe maintaining of the full power supply.

FIG. 7 shows the trend of the signals when a proper activation signal issent to photodiode PH together with noise signal, as those referred toin FIG. 6. It is assumed that when the proper activation signal isreceived by photodiode PH, the value of voltage VA2 and the conductionof transistor MF1 are sufficient or keeping the circuits in a stand-bystate, thanks to the previously described performance.

The arrival of the activation signal—that overlaps the noises and has anintensity that is sharply greater than that of the noises—causes anabrupt increase in the amplitude of the signal generated by photodiodePH and in the amplitude of the amplified signal VA1. Notwithstanding theattenuation effect of transistor MF1, the duty-cycle of the sequence ofpulses VC1 output by comparator C1 increases, signal VF1, outputted byfilter F1, exceeds the threshold value VTH2 and signal VC2 switches tohigh logic level, thereby enabling the power supply of logic L and thechecking of the frequency and duration attributes of the receivedsignal. The value of signal VF2, output by filter F2, also slightlyincreases, but more slowly, thanks to the different time constant RC2,and the value of voltage VA2 increases in the same way. It should benoted that, unlike what has been shown for the sake of simplicity andclarity in FIG. 7, the variations of signal VA2 are of a definitelygreater entity (that depends on the gain of amplifier A2) with respectto those of signal VF2. The increase in the value of voltage VA2 causes,through the action of transistor MF1, a greater attenuation of thesignal of photodiode PH, that is sufficient for bringing the output offilter F1 back to a value that is just slightly higher than VTH3.However, before this takes place, signal VC2 remains at high logic levelso as to enable the power supply for a time interval that is sufficientfor permitting logic L to recognize the frequency and the durationattributes of the activation signal and switch the level of signal VL inorder to maintain the power supply even after the decrease of signal VC2as a consequence of the automatic sensitivity control.

It should be noted that, in the event the increase in the amplitude ofthe voltage generated by photodiode PH were also to be caused by anunwanted noise signal, for example owing to a sudden displacementbetween probe 4 and a fluorescent lamp, the consequent supply of logic Lwould be in any case of short duration (as the situation referred to inFIG. 6).

It should furthermore be noted that the trend of signal VF1, shown inFIG. 7, indicates a further decrease, below threshold VTH3, for a shorttime interval that follows the end of the activation signal, when thereis still considerable attenuation, and the subsequent return to a valueslightly higher than threshold VTH3 further to a drop (decrease of VF2and VA2) of the attenuation, yet sufficient for “filtering” noisesignals.

FIG. 8 represents the situation in which a deactivation signal is sentby stationary transceiver unit 10 in the following circumstances:

1) probe 4 is performing a checking cycle and thus there is full powersupply to the circuits (VL is at high logic level), and

2) the noise signals received by photodiode PH cause the attenuation ofthe signal that photodiode PH generates in accordance with thepreviously described performance, thereby preventing the sequence ofpulses VC1 from reaching logic L (VC2 is at low logic level).

The freshly input signal, the intensity of which is particularly high,overlaps the noises and causes an abrupt increase in the amplitude ofthe signal generated by photodiode PH. The performance shown in FIG. 8is similar to that of the example shown in FIG. 7, and signal VC2 isswitched to high logic level and remains so for a short period of time,before the signal of photodiode PH is suitably attenuated. In this case,the effect of the switching of signal VC2 is not that of altering thepower supply of logic L (it is already powered thanks to the action ofsignal VL), but that of enabling—by means of the logic AND circuitG2—logic L to check the frequency and duration attributes of the freshlyinput signal. If, on the basis of these checks, there is identified adeactivation signal, the logic level of signal VL is switched from highto low in such a way so that, further to the subsequent decrease in thelevel of signal VC2 due to the attenuation effect, the power supply oflogic L (and that of the circuits T for generating and transmittingoptical signals) is inhibited. On the contrary, the checks end, whensignal VC2 returns to low logic level, if the deactivation signal hasnot been identified.

Obviously the probability that, in the course of the short timeintervals when VC2 is at high logic level, there be a noise signal withthe frequency and duration attributes of an activation signal isextremely low. However, should this unlikely event occur, it could causethe undesired activation of probe 4, i.e. the undesired full powersupply of its circuits.

In an identical (and equally unlikely) manner it could take place that,in the course of short time intervals when VC2 is at high logic level,there be the reception of a noise signal with the attributes of adeactivation signal that, identified as such, could interrupt the supplyof power to the circuits of probe 4 while a checking cycle is takingplace and cause foreseeable negative consequences.

By way of experiment it has occurred that, while the fluorescent lampswith electronic reactor emit noises 10 having considerably higherfrequencies than the frequencies of the proper activation anddeactivation signals, noises emitted by lamps with non-electronicreactor can have frequencies that are closer to those of the formerproper signals. Typically the lamps of the second type emit noises withan intensity that periodically takes a value near zero for a relativelynon negligible time interval (typically near a millisecond), as thepower supply voltage periodically assumes the zero value.

FIG. 9 schematically represents filter F1, shown in FIGS. 2 and 5, andadditional attenuation devices with an additional filtering unit FA,connected in parallel to filter F1. Filter F and unit FA togetherachieve an “asiimetric” filter F1′ that enables to solve the problem ofundesired activations and deactivations of probe 4. Filter F1′ includestwo low pass filters, one (F1) consists of resistor RES1 and capacitorCON1 and the other consists of resistor RES2 and capacitor CON2.Moreover, unit FA includes a comparator C3, that compares the signal atits input with a threshold VTH4, and a diode D1, that, for the sake ofsimplicity in the description, is considered as ideal. The filterconsisting of components RES2 and CON2 has a lower time constant withrespect to that of filter F1.

On reception of a signal with suitable intensity and negligibleinterruptions, the signal outputted by the filter consisting of RES2 andCON2 increases more rapidly with respect to the one outputted by F1,until it exceeds threshold value VTH4 and switches the output ofcomparator C3 to high logic level. Thus diode D1 is turned off. In thiscase filter F1′ substantially acts as filter F1, in other words in themanner described with reference to FIGS. 2 and 5. On the contrary, ifthe received signal has significant interruptions, at every interruptionthe value of the voltage at the input of comparator C3 falls below thevalue of VTH4, switching the output of comparator C3 to low logic level.Thus, diode D1 periodically conducts and enables the periodic dischargeof capacitor CON1. As a consequence, signal F1 does not reach thresholdvalue VTH2 and the power supply of logic L is not enabled and/or signalVC1 does not reach logic L. Therefore, the use of filter F1′ in FIG. 9in a circuit as the one of FIG. 2, or FIG. 5, prevents noise signalswith significant interruptions, as those emitted by fluorescent lampswith non-electronic reactor, to cause the even temporary power supply oflogic L or the even temporary enabling of the signal frequency checks.It should be realized that, as previously mentioned, these noise signalsare, among the noises emitted by the fluorescent lamps, those which havefrequency and regularity attributes that have a relatively higherprobability (even though in absolute very low) of approaching theattributes of the activation and deactivation signals. Thus, as with theuse of filter F1′ the power supply of logic L is not even enabled for alimited time or, if the device is in the transmission phase, the checksof the signal frequency are not even enabled for a limited time,substantially there is no risk of possible unwantedactivation/deactivation. Obviously, the presence of filter F1′ incombination with the automatic sensitivity control enabled by thearrangement of FIG. 5 gives simultaneous protection against the noisesignals both at lower frequencies (comparable with theactivation/deactivation frequencies) and at higher frequencies (likethose emitted by fluorescent lamps with electronic reactor), in thelatter case enabling undesired power supply of just logic L for sporadicand very short intervals of time (typically shorter than half a second)that are substantially negligible in view of the correct consumption ofenergy of battery 12.

FIG. 10 is a schematic and partial diagram of a remote transceiver unit8 according to another embodiment of the invention.

The circuit comprises, in addition to the components described withreference to FIGS. 5 and 9, a LED LD that enables to visually check thestate of probe 4 and indicate the presence of noises, and a connectionsection SC that includes: a programming unit DS, for example a manuallyoperated switch (or “dip switch”) with two selectors, more specificallyswitches SW1 and SW2, three resistors RES3, RES4, RES5, a comparator C4for comparing the signal at its input with a threshold value VTH5, and afield effect transistor MF2. Furthermore, FIG. 10 schematically showsthe detecting devices 13 (i.e. a microswitch) and the associatedconnections to the connection section SC.

When switch SW2 is open (it can be operated, for example, in a manualway) and the apparatus is transmitting, the turning on of LED LDmonitors the deflection of arm 7 as a consequence of contact betweenfeeler 6 and a piece 1. In fact, when arm 7 is not deflected (there isno contact between feeler 6 and piece 1), microswitch 13 is closed: inthis condition, the signal at the non-inverting input of comparator C4is low, thus, transistor MF2 is held off and LED LD is off.

On the contrary, when arm 7 is deflected, microswitch 13 is open andthus at the non-inverting input of comparator C4 there is a signal thatexceeds the threshold value VTH5 and enables transistor MF2 to conduct.In this case, the voltage at the ends of LED LD causes its turning onfor visually displaying that contact between feeler 6 and the surface ofpiece 1 has taken place. The voltage at the output of comparator C4 isalso sent to logic L, that detects that contact has taken place andaccordingly drives the circuits T for generating and transmittingoptical signals.

If switch SW2 is closed, when the logic is powered (signal A is at highlogic level), transistor MF2 conducts and LED LD is on, regardless ofthe condition of microswitch 13. Switch SW2 can be turned off in thephase of assembly and setting up of probe 4 on machine tool 2 for thepurpose of allowing to visually check through LED LD whether, in thespecific position in which the probe will be mounted on the machinetool, the remote transceiver unit 8 is subject to noises. In fact, inthis phase the only cause of the supply of power to logic L (signal VAis at high logic level), that can be identified by the turning on of LEDLD, is noises. In the event this occurs, switch SW1 can be turned off(for example, it can be manually operated), the latter allows signals tobe sent to amplifier A2 and to the additional filtering unit FA forenabling the associated automatic sensitivity control and “asimmetric”filtering functions. After a specific time has elapsed from the start ofthe noise signal, as a consequence of the switching of signal VA to lowlogic level, the turning off of LED LD visually monitors that thecircuit has provided an efficacious protection against the noises.

When the setting up phase ends, switch SW2 is opened so LED LD cancontinue to visually monitor the condition of arm 7 of probe 4. On thecontrary, switch SW1 can be either turned off or on depending onwhether—on the basis of the detections made in the setting up phase—itbe considered advisable to enable the automatic sensitivity control and“asimmetric” filtering functions for limiting the power supply timeperiods of logic L and minimize unwanted consumption of energy ofbattery 12 and the risk of unwanted activations and deactivations.

Thus, the so far described embodiments of the remote transceiver unit 8enable, in a particularly simple and efficacious way, to achievesubstantially negligible unwanted consumptions of energy of battery 12due, for example, to noise signals that can be emitted by fluorescentlamps, and reduce practically to zero the probability that these noisesignals be the cause of an accidental activation or deactivation ofprobe 4.

Obviously, the components of unit 8, herein described and illustrated inan extremely schematic way, can be achieved in various known wayswithout departing from the scope of the present invention. This alsoapplies to the other units and components shown in the figures, as, forexample, the detecting devices 13, which can include switches ortransducers of a known type.

Systems including other aspects with respect to what is hereindescribed, as for example, insofar as the attributes of the activationand deactivation signals identified by the logic are concerned also fallwithin the scope of the invention. These attributes may include specificcodings of the signals, not necessarily bound to frequency and/orduration (number of pulses) of the signals.

Furthermore, even though the figures and the associated descriptionrefer to a transceiver system of infrared signals, the present inventioncan be applied—without substantial modifications—to systems thattransmit signals at other frequencies, for example in the radiofrequency range.

What is claimed is:
 1. A system for detecting linear dimensions of aworkpiece comprising: a checking probe with detecting devices; a powersupply connected to the checking probe; a remote transceiver unit,integral with the probe, connected to the detecting devices and to thepower supply, and adapted for wireless transmission of signalsindicative of the state of the probe; and a stationary transceiver unit,adapted for wireless transmission of activation signals to said remotetransceiver unit, the remote transceiver unit comprising receivingdevices adapted for receiving the wireless transmitted signals, aprocessing section connected to the receiving devices and to the powersupply and adapted for generating an enable signal, a switching unitconnected to the processing section and to the power supply, andadditional sections connected to the switching unit, the switching unitbeing adapted for receiving the enable signal and, on the basis of thissignal, controlling the power supply of at least one of said additionalsections, wherein the processing section includes attenuation devicesadapted for inhibiting the generation of the enable signal based onattributes of the signals that the receiving devices have received. 2.The system according to claim 1, wherein said attenuation devicesinclude at least a delay generator for enabling the generation of theenable signal as the attributes of the signals received by the receivingdevices vary, and for inhibiting the generation of said enable signalafter a predetermined delay time based on said attributes.
 3. The systemaccording to claim 1, wherein the processing section includes at least afirst amplifier connected to the receiving devices for generating anamplified signal, and the attenuation devices include elements of afeedback circuit for attenuating the intensity of the amplified signal.4. The system according to claim 3, wherein the receiving devices areadapted for transmitting a periodic signal to said first amplifier, saidfeedback circuit being connected to the input of said first amplifierfor reducing the amplitude of said periodic signal based on theamplitude of the amplified signal.
 5. The system according to claim 3,wherein said additional sections of the remote transceiver unit includea logic processing unit, the switching unit being connected to the logicprocessing unit for connecting the power supply to the logic processingunit.
 6. The system according to claim 5, wherein the remote transceiverunit includes an enable device connected to the processing section andto the logic processing unit and adapted for receiving said enablesignal for enabling the transmission to the logic processing unit of aprocessed signal with attributes that match those of the signal receivedby the receiving devices.
 7. The system according to claim 6, whereinsaid attributes of the processed signal include frequency and duration.8. The system according to claim 7, wherein said processing sectionincludes a first comparator connected to said first amplifier andadapted for providing said processed signal, a first low pass filterconnected to the first comparator, a second comparator connected to saidfirst low pass filter and adapted for providing said enable signal, theelements of the feedback circuit including a second low pass filterconnected to the first comparator, a second amplifier connected to thesecond low pass filter, and an attenuation unit connected to the outputof the second amplifier and to the input of said first amplifier.
 9. Thesystem according to claim 8, wherein said attenuation unit includes afield effect transistor.
 10. The system according to claim 3, whereinsaid processing section includes a first comparator connected to saidfirst amplifier and adapted for generating a processed signal, a firstlow pass filter connected to the first comparator, and a secondcomparator adapted for receiving a signal from said at least one lowpass filter and providing said enable signal, the attenuation devicesincluding an additional filtering unit connected between the first andthe second comparator, in parallel to said first low pass filter, andadapted for altering the signal received by said second comparator fordetecting interruptions in the processed signal.
 11. The systemaccording to claim 1, wherein said stationary transceiver unit and saidremote transceiver unit are adapted for transmitting and receivingoptical radiations.
 12. The system according to claim 11, wherein saidstationary transceiver unit and said remote transceiver unit are adaptedfor transmitting and receiving optical radiations in the infrared range.13. The system according to claim 12, wherein the receiving devicesinclude at least a photodiode adapted for receiving infrared radiationsand generating a corresponding alternating signal, the processingsection of the remote transceiver unit being adapted for processing saidalternating signal for generating the enable signal.
 14. The systemaccording to claim 1, wherein the remote transceiver unit includes anLED and a coupling section between the LED, the switching unit and thedetecting devices, said coupling section including a programming unitwith at least a switch, the LED being adapted for visually andalternatively indicating modifications in the state of the probe or thepower supply condition of the probe.
 15. The system according to claim14, wherein the programming unit is of the manually operated type andincludes at least an additional switch, connected to the switching unitand to the attenuation devices, for enabling or inhibiting saidattenuation devices.
 16. The system according to claim 1, wherein saidattenuation devices include at least a delay generator for enabling thegeneration of the enable signal as the attributes of the signalsreceived by the receiving devices vary, and for inhibiting thegeneration of said enable signal after a predetermined delay time basedon said attributes, and wherein the processing section includes at leasta first amplifier connected to the receiving devices for generating anamplified signal, and the attenuation devices include elements of afeedback circuit for attenuating the intensity of the amplified signal.17. The system according to claim 16, wherein the receiving devices areadapted for transmitting a periodic signal to said first amplifier, saidfeedback circuit being connected to the input of said first amplifierfor reducing the amplitude of said periodic signal based on theamplitude of the amplified signal.
 18. The system according to claim 16,wherein said additional sections of the remote transceiver unit includea logic processing unit, the switching unit being connected to the logicprocessing unit for connecting the power supply to the logic processingunit.
 19. The system according to claim 18, wherein the remotetransceiver unit includes an enable device connected to the processingsection and to the logic processing unit and adapted for receiving saidenable signal for enabling the transmission to the logic processing unitof a processed signal with attributes that match those of the signalreceived by the receiving devices.
 20. The system according to claim 19,wherein said attributes of the processed signal include frequency andduration.
 21. The system according to claim 20, wherein said processingsection includes a first comparator connected to said first amplifierand adapted for providing said processed signal, a first low pass filterconnected to the first comparator, a second comparator connected to saidfirst low pass filter and adapted for providing said enable signal, theelements of the feedback circuit including a second low pass filterconnected to the first comparator, a second amplifier connected to thesecond low pass filter, and an attenuation unit connected to the outputof the second amplifier and to the input of said first amplifier. 22.The system according to claim 21, wherein said attenuation unit includesa field effect transistor.
 23. The system according to claim 16, whereinsaid processing section includes a first comparator connected to saidfirst amplifier and adapted for generating a processed signal, a firstlow pass filter connected to the first comparator, and a secondcomparator adapted for receiving a signal from said at least one lowpass filter and providing said enable signal, the attenuation devicesincluding an additional filtering unit connected between the first andthe second comparator, in parallel to said first low pass filter, andadapted for altering the signal received by said second comparator fordetecting interruptions in the processed signal.